The development of clinically applicable biomarkers for cancer, particularly minimally invasive biomarkers, has been an insurmountable challenge for a number of years. Recent discovery of circulating microRNAs provided some hope; these microRNAs have been suggested to be biomarkers of breast, lung, and prostate cancer. The source of these circulating microRNAs is unknown but is believed to be derived from cancer either through secreted exosomes or released by dying cancer cells. Intriguingly, the levels of several microRNAs are lower in the serum of cancer patients compared to healthy suggesting that cancer is either causing destruction of the adjoining normal tissues from which these microRNAs are normally secreted or it is influencing the expression and secretion of these microRNAs from distant organs. Our recent studies support the latter possibility; serum from breast cancer patients, who are clinically disease-free, displayed elevated levels of miR-451 and miR-101 but lower levels of miR-370, miR-574-3p, miR-342-3p, and miR-197. Additionally, serum from patients contained elevated levels of U6 and 5S, which are small RNAs transcribed by RNA polymerase III. The following hypotheses will be tested in this proposal: Chronic inflammation-like condition in cancer patients lead to permanent changes in microRNA/small RNA expression in distant organs, particularly in organs with regenerative capacity such as liver. Cancer or host-response to cancer causes elevated levels of circulating cytokines such as interleukin 6 (IL-6), which may mediate the long-term effects of cancer on microRNA expression in distant organs. Consequently, distinct microRNA and U6 RNA levels persist in the serum of cancer patients even after these patients are clinically free of the disease. Experiments described in two specific aims will test the above hypotheses: I) Determine whether genes corresponding to microRNAs/small RNA differentially expressed in the serum of cancer bearing animals show altered expression, histone modifications, and RNA polymerase occupancy in liver and lungs. The animal models of breast cancer including MMTV-PyMT, MMTV-neu and xenografts with ER1- positive and ER1-negative breast cancer cells along with appropriate controls will be used to measure serum microRNA profile and cancer-associated changes in microRNA, U6 and 5S expression in liver and lungs. Recruitment of modified histones and RNA polymerase II/III to regulatory regions of U6, 5S, and select microRNA genes in liver and lungs will be measured in control and cancer bearing animals. Serum will be analyzed for mouse IL-6. II) Investigate prospectively whether serum U6, 5S and select miRNA levels change during breast cancer treatment. Serum from breast cancer patients prior to starting neoadjuvant therapy, immediately after completing therapy but before surgery, and after surgery will be examined for U6, 5S RNA and select microRNAs. If cancer is the primary source of the above microRNA/ small RNAs in the serum, their levels should drop after neoadjuvant therapy and/or surgery. If specific microRNA is host -derived and changes in its expression in distant organ is permanent, therapy should not influence its expression. Long-term goal is to determine cancer-induced collateral damage to other organs and how this damage may influence overall health of cancer patients. PUBLIC HEALTH RELEVANCE: This proposal will examine whether microRNAs and small RNAs detected in the serum of breast cancer patients originate from cancer or from the distant organs. It is likely that the chronic inflammation-like condition in cancer patients may cause permanent gene expression changes in liver and lungs, which leads to altered levels of serum microRNAs and small RNAs. The circulating microRNAs may be the invisible long-arm of cancer that reaches distant organs as circulating microRNAs can fuse with heterotypic cells and influence gene expression.